[llvm] f8de161 - [KeyInstr][SimplifyCFG] Remap atoms when folding br to common succ into pred (#133482)
via llvm-commits
llvm-commits at lists.llvm.org
Tue May 6 07:03:24 PDT 2025
Author: Orlando Cazalet-Hyams
Date: 2025-05-06T15:03:20+01:00
New Revision: f8de1618cc3349829ed5ab699413dcb84451e0c7
URL: https://github.com/llvm/llvm-project/commit/f8de1618cc3349829ed5ab699413dcb84451e0c7
DIFF: https://github.com/llvm/llvm-project/commit/f8de1618cc3349829ed5ab699413dcb84451e0c7.diff
LOG: [KeyInstr][SimplifyCFG] Remap atoms when folding br to common succ into pred (#133482)
SimplifyCFG folds `d` into preds `b` and `c`.
+---------------+
| |
+--> b --+ |
| v v
--> a d --> e --> f -->
| ^ ^
+--> c --+ |
| |
+---------------+
Remap source atoms so that the duplicated instructions are analysed
independently to determine is_stmt positions.
The pull request contains a discussion covering various edge cases here:
https://github.com/llvm/llvm-project/pull/133482/files#r2039519348
The summary of the discussion is that we could avoid remapping when there's a
single pred, but we decided that it's still a trade off, and not worth the
additional complexity right now.
RFC:
https://discourse.llvm.org/t/rfc-improving-is-stmt-placement-for-better-interactive-debugging/82668
Added:
llvm/test/DebugInfo/KeyInstructions/Generic/simplifycfg-branch-fold.ll
Modified:
llvm/include/llvm/IR/DebugLoc.h
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
Removed:
################################################################################
diff --git a/llvm/include/llvm/IR/DebugLoc.h b/llvm/include/llvm/IR/DebugLoc.h
index 255ceb9571909..ffb8ed458e36b 100644
--- a/llvm/include/llvm/IR/DebugLoc.h
+++ b/llvm/include/llvm/IR/DebugLoc.h
@@ -170,6 +170,16 @@ namespace llvm {
LLVMContext &Ctx,
DenseMap<const MDNode *, MDNode *> &Cache);
+ /// Return true if the source locations match, ignoring isImplicitCode and
+ /// source atom info.
+ bool isSameSourceLocation(const DebugLoc &Other) const {
+ if (get() == Other.get())
+ return true;
+ return ((bool)*this == (bool)Other) && getLine() == Other.getLine() &&
+ getCol() == Other.getCol() && getScope() == Other.getScope() &&
+ getInlinedAt() == Other.getInlinedAt();
+ }
+
unsigned getLine() const;
unsigned getCol() const;
MDNode *getScope() const;
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 33af582a9e0a9..89709e1303651 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -73,6 +73,7 @@
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/LockstepReverseIterator.h"
#include "llvm/Transforms/Utils/ValueMapper.h"
@@ -1129,13 +1130,17 @@ static void cloneInstructionsIntoPredecessorBlockAndUpdateSSAUses(
Instruction *NewBonusInst = BonusInst.clone();
- if (!isa<DbgInfoIntrinsic>(BonusInst) &&
- PTI->getDebugLoc() != NewBonusInst->getDebugLoc()) {
- // Unless the instruction has the same !dbg location as the original
- // branch, drop it. When we fold the bonus instructions we want to make
- // sure we reset their debug locations in order to avoid stepping on
- // dead code caused by folding dead branches.
- NewBonusInst->setDebugLoc(DebugLoc());
+ if (!isa<DbgInfoIntrinsic>(BonusInst)) {
+ if (!NewBonusInst->getDebugLoc().isSameSourceLocation(
+ PTI->getDebugLoc())) {
+ // Unless the instruction has the same !dbg location as the original
+ // branch, drop it. When we fold the bonus instructions we want to make
+ // sure we reset their debug locations in order to avoid stepping on
+ // dead code caused by folding dead branches.
+ NewBonusInst->setDebugLoc(DebugLoc());
+ } else if (const DebugLoc &DL = NewBonusInst->getDebugLoc()) {
+ mapAtomInstance(DL, VMap);
+ }
}
RemapInstruction(NewBonusInst, VMap,
@@ -1182,6 +1187,19 @@ static void cloneInstructionsIntoPredecessorBlockAndUpdateSSAUses(
U.set(NewBonusInst);
}
}
+
+ // Key Instructions: We may have propagated atom info into the pred. If the
+ // pred's terminator already has atom info do nothing as merging would drop
+ // one atom group anyway. If it doesn't, propagte the remapped atom group
+ // from BB's terminator.
+ if (auto &PredDL = PTI->getDebugLoc()) {
+ auto &DL = BB->getTerminator()->getDebugLoc();
+ if (!PredDL->getAtomGroup() && DL && DL->getAtomGroup() &&
+ PredDL.isSameSourceLocation(DL)) {
+ PTI->setDebugLoc(DL);
+ RemapSourceAtom(PTI, VMap);
+ }
+ }
}
bool SimplifyCFGOpt::performValueComparisonIntoPredecessorFolding(
diff --git a/llvm/test/DebugInfo/KeyInstructions/Generic/simplifycfg-branch-fold.ll b/llvm/test/DebugInfo/KeyInstructions/Generic/simplifycfg-branch-fold.ll
new file mode 100644
index 0000000000000..75a05ad931707
--- /dev/null
+++ b/llvm/test/DebugInfo/KeyInstructions/Generic/simplifycfg-branch-fold.ll
@@ -0,0 +1,91 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt %s -S -passes=simplifycfg -bonus-inst-threshold=2 | FileCheck %s
+
+;; +---------------+
+;; | |
+;; +--> b --+ |
+;; | v v
+;; --> a d --> e --> f -->
+;; | ^ ^
+;; +--> c --+ |
+;; | |
+;; +---------------+
+
+;; Block d gets folded into preds b and c. Check the cloned instructions get
+;; remapped DILocation atomGroup numbers in each of the preds. Additionally
+;; check that the branches each inherit the atomGroup of the folded branch.
+
+declare i32 @g(...)
+define void @f(i1 %c0, i1 %c1, i1 %c2, i32 %x, i32 %y) !dbg !17 {
+; CHECK-LABEL: define void @f(
+; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]], i1 [[C2:%.*]], i32 [[X:%.*]], i32 [[Y:%.*]]) !dbg [[DBG6:![0-9]+]] {
+; CHECK-NEXT: [[A:.*:]]
+; CHECK-NEXT: br i1 [[C0]], label %[[B:.*]], label %[[C:.*]]
+; CHECK: [[B]]:
+; CHECK-NEXT: [[AND_OLD:%.*]] = and i32 [[X]], [[Y]], !dbg [[DBG8:![0-9]+]]
+; CHECK-NEXT: [[CMP_OLD:%.*]] = icmp eq i32 [[AND_OLD]], 0, !dbg [[DBG9:![0-9]+]]
+; CHECK-NEXT: [[OR_COND1:%.*]] = select i1 [[C1]], i1 true, i1 [[CMP_OLD]], !dbg [[DBG10:![0-9]+]]
+; CHECK-NEXT: br i1 [[OR_COND1]], label %[[F:.*]], label %[[E:.*]], !dbg [[DBG11:![0-9]+]]
+; CHECK: [[C]]:
+; CHECK-NEXT: [[AND:%.*]] = and i32 [[X]], [[Y]], !dbg [[DBG12:![0-9]+]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[AND]], 0, !dbg [[DBG13:![0-9]+]]
+; CHECK-NEXT: [[OR_COND:%.*]] = select i1 [[C2]], i1 true, i1 [[CMP]], !dbg [[DBG10]]
+; CHECK-NEXT: br i1 [[OR_COND]], label %[[F]], label %[[E]], !dbg [[DBG14:![0-9]+]]
+; CHECK: [[E]]:
+; CHECK-NEXT: [[TMP0:%.*]] = tail call i32 (...) @g()
+; CHECK-NEXT: br label %[[F]]
+; CHECK: [[F]]:
+; CHECK-NEXT: ret void
+;
+a:
+ br i1 %c0, label %b, label %c
+
+b:
+ br i1 %c1, label %f, label %d, !dbg !18
+
+c:
+ br i1 %c2, label %f, label %d, !dbg !18
+
+d:
+ %and = and i32 %x, %y, !dbg !19
+ %cmp = icmp eq i32 %and, 0, !dbg !20
+ br i1 %cmp, label %f, label %e, !dbg !21
+
+e:
+ %7 = tail call i32 (...) @g()
+ br label %f
+
+f:
+ ret void
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.debugify = !{!3, !4}
+!llvm.module.flags = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "a.ll", directory: "/")
+!2 = !{}
+!3 = !{i32 9}
+!4 = !{i32 0}
+!5 = !{i32 2, !"Debug Info Version", i32 3}
+!7 = !DISubroutineType(types: !2)
+!17 = distinct !DISubprogram(name: "f", scope: null, file: !1, line: 1, type: !7, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!18 = !DILocation(line: 10, column: 10, scope: !17)
+!19 = !DILocation(line: 10, column: 10, scope: !17, atomGroup: 1, atomRank: 2)
+!20 = !DILocation(line: 10, column: 10, scope: !17, atomGroup: 2, atomRank: 2)
+!21 = !DILocation(line: 10, column: 10, scope: !17, atomGroup: 2, atomRank: 1)
+;.
+; CHECK: [[META0:![0-9]+]] = distinct !DICompileUnit(language: DW_LANG_C, file: [[META1:![0-9]+]], producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: [[META2:![0-9]+]])
+; CHECK: [[META1]] = !DIFile(filename: "a.ll", directory: {{.*}})
+; CHECK: [[META2]] = !{}
+; CHECK: [[DBG6]] = distinct !DISubprogram(name: "f", scope: null, file: [[META1]], line: 1, type: [[META7:![0-9]+]], scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: [[META0]], retainedNodes: [[META2]])
+; CHECK: [[META7]] = !DISubroutineType(types: [[META2]])
+; CHECK: [[DBG8]] = !DILocation(line: 10, column: 10, scope: [[DBG6]], atomGroup: 5, atomRank: 2)
+; CHECK: [[DBG9]] = !DILocation(line: 10, column: 10, scope: [[DBG6]], atomGroup: 6, atomRank: 2)
+; CHECK: [[DBG10]] = !DILocation(line: 10, column: 10, scope: [[DBG6]])
+; CHECK: [[DBG11]] = !DILocation(line: 10, column: 10, scope: [[DBG6]], atomGroup: 6, atomRank: 1)
+; CHECK: [[DBG12]] = !DILocation(line: 10, column: 10, scope: [[DBG6]], atomGroup: 3, atomRank: 2)
+; CHECK: [[DBG13]] = !DILocation(line: 10, column: 10, scope: [[DBG6]], atomGroup: 4, atomRank: 2)
+; CHECK: [[DBG14]] = !DILocation(line: 10, column: 10, scope: [[DBG6]], atomGroup: 4, atomRank: 1)
+;.
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